To convert an expansion rate of an image, it is necessary to obtain an output image signal by determining pixel data having a phase different from that of pixel data of an input image signal. In this case, by using an expansion rate of the post-conversion image, a phase relation of a pixel of the output image signal with respect to a pixel of the input image signal is determined uniquely.
Conventionally a method has been proposed by which when obtaining pixel data of an output image signal from pixel data of an input image signal in order to convert an expansion rate of an image, coefficient data for an estimate equation that corresponds to each phase of a pixel of the output image signal with respect to a pixel of the input image signal is stored in a memory beforehand and read to obtain pixel data of the output image signal based on the estimate equation using the coefficient data.
If an expansion rate of the post-conversion image is different, a different phase relation of the pixel of the output image signal is given with respect to the pixel of the input image signal. Therefore, in the method for storing the coefficient data for the estimate equation in the memory, to convert the expansion rate into various values, it is necessary to store items of coefficient data in accordance with these various values of the expansion rate in the memory. In such a case, therefore, it is necessary to provide a memory for storing a lot of items of coefficient data, thus leading to a problem of an expensive conversion device etc.
To solve this problem, the present applicant has earlier proposed a device that can produce coefficient data to be used in an estimate equation from coefficient seed data on the basis of phase information to eliminate a necessity of a memory for storing a lot of items of coefficient data to convert an expansion rate into various values (see Jpn. Pat. Appln. KOKAI Publication No. 2002-196737).
For example, by changing an expansion rate of an image consecutively, electronic zoom can be realized. This electronic zoom has had such problems that blur develops in an expanded still image as a whole, that transition from a still image to an expanded moving image encounters fold-back distortion, and that noise, if any, in an input image signal becomes conspicuous in an expanded image. Besides, if the expansion rate of the image changes rapidly in zooming, a processing range of the input image signal varies significantly over a period of time, thus causing a problem that no visually smooth zoom image can be obtained.